1. Field of the Invention
The present invention relates to a torque limiter, a display screen turning apparatus comprising a torque limiter and a television set including a torque limiter.
2. Description of the Background Art
A torque limiter having a spring member is known in general, as disclosed in each of Japanese Utility Model Laying-Open No. 5-15140 (1993), Japanese Patent Laying-Open No. 6-180899 (1994) and Japanese Patent Laying-Open No. 6-176444 (1994), for example.
The aforementioned Japanese Utility Model Laying-Open No. 5-15140 discloses a reel driving apparatus comprising a lower coupling gear, provided with a first boss, receiving power transmitted thereto, an upper coupling gear provided with a second boss into which an upper portion of the first boss is inserted and a clutch spring (spring member) inserted into the first and second bosses and arranged to be held between the lower and upper coupling gears. The reel driving apparatus described in Japanese Utility Model Laying-Open No. 5-15140 is so formed that the clutch spring is wound to transmit power to the upper coupling gear when normal rotation is transmitted to the lower coupling gear. Further, the reel driving apparatus is so formed that the clutch spring is separated not to transmit the power to the upper coupling gear when reverse rotation is transmitted to the lower coupling gear.
The aforementioned Japanese Patent Laying-Open No. 6-180899 discloses a clutch structure comprising a support shaft, a support plate rotatably mounted on the lower end portion of the support shaft, a pulley rotatably arranged so that driving force is transmitted thereto and a friction member arranged between the upper surface of the support plate and the lower surface of the pulley. The clutch structure disclosed in Japanese Patent Laying-Open No. 6-180899 further comprises a clutch gear rotatably mounted on the upper end portion of the support shaft and a coil spring applying urging force between the pulley and the clutch gear. The clutch structure described in Japanese Patent Laying-Open No. 6-180899 is so formed that the pulley is brought into pressure contact with the friction member due to downward urging force of the coil spring so that constant torque is generated when driving force applied to the pulley is transmitted to the support plate through the friction member and the driving force is transmitted to the clutch gear through the support plate and the support shaft.
The aforementioned Japanese Patent Laying-Open No. 6-176444 discloses a felt clutch mechanism comprising a torque generating spring, an upper rotating member pressed downward by the torque generating spring, a felt member coming into contact with the lower surface of a first member and a lower rotating member to which the lower surface of the felt member is bonded/fixed. The felt clutch mechanism described in Japanese Patent Laying-Open No. 6-176444 is so formed that the upper rotating member is brought into pressure contact with a friction member due to downward urging force of the torque generating spring so that constant torque is generated when driving force applied to the lower rotating member is transmitted to the upper rotating member through the friction member and the driving force is transmitted to the upper rotating member.
In the reel driving apparatus described in the aforementioned Japanese Utility Model Laying-Open No. 5-15140, however, only either rotation (normal direction) is transmitted from the lower coupling gear to the upper coupling gear. Therefore, bidirectional rotation cannot be transmitted.
In the clutch structure disclosed in the aforementioned Japanese Patent Laying-Open No. 6-180899, the friction member must be provided separately from the support shaft, the support plate, the pulley and the coil spring, in order to generate the constant torque. Therefore, the number of components is disadvantageously increased.
In the felt clutch mechanism described in the aforementioned Japanese Patent Laying-Open No. 6-176444, the felt member must be provided separately from the upper rotating member, the lower rotating member and the torque generating spring, in order to generate the constant torque. Therefore, the number of components is disadvantageously increased.